Films of various sorts have been used as protective coverings for buildings. Films are often used to bar water while allowing sunlight in such as greenhouse films. The various films known, are directed to various different applications depending on the properties of the film. The composition of the film is provided to meet a specific requirement of the end use.
U.S. Pat. No. 4,961,297 discloses a greenhouse exterior film. The film is provided in the form of transparent building panels which transmit solar light and heat into the building enclosure. Each panel is supported by a rigid framework and is connected to a support system of the building. This patent is not concerned with providing additional insulation or breathability to an already existing structure or providing additional insulation to a building under construction. This prior art disclosure does not consider providing vapor permeability while preventing air infiltration and water infiltration.
U.S. Pat. No. 4,397,122 proposes a method of protecting a construction to protect the interior against the action of wind and rain. This patent proposes the use of a knitted fabric of glass fiber threads. The proposed fabric is intended as a temporary measure only and this patent fails to propose a barrier film which allows vapor transmission but provides protection to a structure by preventing air infiltration and water infiltration.
U.S. Pat. No. 4,206,575 proposes a covering for mobile homes. The covering includes an outer layer of waterproofed material and an inner layer of film-type insulating material bonded to the outer layer. This covering has the possibility of trapping water vapor between the mobile home and the outer waterproof layer. This covering would not be useful as an protective layer for a house or the like in that moisture would build up between the covering and the vapor barrier of the structure.
The product sold under the trade name TYVEK by the company DuPont has been proposed for use as a house wrap, to provide protection and insulation. TYVEK is a non-woven fabric of polyethylene fibers. The fabric allows vapor to pass through the porous fabric however the fabric generally provides a barrier to air and water. These desirable attributes are offset by the expense involved in manufacture, making it higher in cost than extruded films. Also the fabric itself, although effective when installed, is somewhat more difficult to cut, fit and connect adjacent strips than typical extruded films.
Similar film type products are also offered by other companies for house wrap barrier and insulation purposes. These additional products include TYPAR offered by the Reemay Company and BARRICADE, offered by the Simplex Company among others. All of the products have some drawbacks including cost of manufacture and ease of insulation as well as an effective balance of properties between resistance to water penetration and high vapor transmission without allowing direct admission of air. These often involve intricate woven configurations, coatings on either or both sides and other manufacturing processes.
Problems with the use of products as noted above have been noted in the literature (See for example Energy Design Update--August 1996 pages 5-6). Indeed, the mechanism for allowing vapor to pass through and otherwise to provide a barrier, is still not understood. It is known that perforating films from spun bonded films like Typar and woven films like Amowrap and smooth films like R-wrap have been demonstrated. However, it is also known that these perforated films have not worked satisfactorily in actual practice.